1. Field of the Invention
This invention relates generally to traps for collecting and removing condensable aluminum chloride vapor from a gas stream to control the build-up of aluminum chloride in vacuum pump lines, valves, and other components downstream from aluminum etching chambers, and more particularly to an improved aluminum chloride trap containing a disposable element for cooling and condensing condensable aluminum chloride vapor byproducts from an aluminum etch system and retaining the condensed aluminum chloride solids within the disposable element, wherein the disposable element can be easily and quickly removed for the safe and rapid removal and disposal of the condensed aluminum chloride solids.
2. Description of the Prior Art
In a typical aluminum etching process for producing components for semiconductor devices, a silicon wafer or other substrate having a film of aluminum on its top surface is positioned in a reaction chamber, and the chamber is evacuated to a vacuum of about 10 millitorr via a turbo pump and a mechanical pump which are connected to a reaction chamber via a foreline. A photoresist having a particular pattern is placed on the aluminum surface to protect part of the aluminum film. The exposed part of the aluminum film that is not protected by the photoresist is then etched by employing a reactive, chlorine-containing gas such as chlorine (Cl.sub.2) or boron trichloride (BCl.sub.3). Typically, the etching reaction is plasma-enhanced, where the reaction between the chlorine-containing gas and the aluminum film is enhanced by applying rf power to the reaction chamber to create a plasma comprising the atomic constituents of the reactive gas in high energy states in the chamber. The generation of the plasma also causes the reaction chamber to heat up, typically to a temperature of 100 to 150.degree. C. The plasma-assisted reaction between the aluminum film and the chlorine-containing reaction gas etches aluminum from the exposed areas of the aluminum film, resulting in the formation of condensable aluminum chloride vapor (AlCl.sub.3) byproducts. The reaction chamber effluent, which contains the condensable aluminum chloride vapor in addition to excess chlorine-containing reaction gas, is then removed from the reaction chamber by an applied vacuum from a vacuum pump. An exhaust line leading from the vacuum pump then directs the effluent to a scrubber, where the condensable aluminum chloride vapor and any excess chlorinated reaction gases are destroyed. A wet scrubber is often employed to treat the effluent with water to remove the condensable aluminum chloride vapor and excess chlorinated reaction gas from the effluent. Alternatively, a dry scrubber may be employed to destroy excess chlorine-containing reaction gases from the effluent, however, the dry scrubber is not able to destroy the condensable aluminum chloride vapor byproduct.
The condensable aluminum chloride vapor byproduct in the conventional aluminum etching systems described above cause problems downstream from the reaction chamber, because they condense, solidify, and deposit upon contact with cool surfaces, such as the cooler interior surfaces of the vacuum forelines and exhaust lines that are used to convey the effluent gas away from the reaction chambers, as well as in other components of the vacuum conduit system of the etching system. Such buildup of solid aluminum chloride downstream from the etching chamber can partially or even entirely clog the pipes, thus reducing vacuum conductance, and can cause piping, pumps, scrubbers and other equipment used in the etching system to be functionally impaired or inoperative and in need of frequent maintenance. Solid aluminum chloride buildup can also flake apart and fall off the piping surfaces and migrate back into the reaction process chamber to become a source of contamination in the semiconductor device manufacturing process.
Typically, the vacuum in the foreline of an aluminum etching system is approximately 500 millitorr, and consequently it is necessary to heat the forelines to a temperature of about 70.degree. C. in order to keep condensable aluminum chloride vapor in the vapor phase so that the condensable aluminum chloride vapor can be removed from the chamber and the foreline by the applied vacuum. However, the pressure in the exhaust line between the pump and the scrubber is typically 760 torr, and therefore it is necessary to heat the exhaust lines to even higher temperatures, typically around 105.degree. C., to keep the condensable aluminum chloride vapor in the vapor phase as the effluent flows through the exhaust lines. If either the foreline, the exhaust line, or both are not maintained at the proper temperature, the condensable aluminum chloride vapor will cool, condense, and solidify, and the condensed aluminum chloride solids will build up along the interior surfaces of the vacuum conduit system, resulting in the diminished function or clogging of the vacuum source.
In order to prevent condensation and solidification and build-up of condensed aluminum chloride solids in the forelines and exhaust lines in aluminum etching systems, heater jackets can be wrapped around such piping to maintain the forelines and exhaust lines at an elevated temperature, thereby preventing condensation and solidification of condensable aluminum chloride vapor on the inside surfaces of such piping. However, depending on the length of the forelines and exhaust lines in the etching system, the use of heating jackets can be quite costly. For example, in some etching systems the reaction chamber may be located on one floor of a building while the vacuum pump and scrubber may be located one or more floors above or below the reaction chamber. Consequently, the foreline, the exhaust line, or both may be 10 feet or longer. In such situations, the use of heating jackets could be cost prohibitive. Therefore, as a less costly alternative, heating tape is often used in place of heating jackets to heat the forelines and exhaust lines. However, the use of heating tape also has drawbacks in that it can be difficult to completely and effectively wrap the lines, and consequently gaps are often left between sections of the heating tape. Such gaps between sections of heating tape on a poorly wrapped pipe result in "cold spots," where the condensable aluminum chloride vapor condenses on the inside of the pipe.
Additional measures used to control the buildup of solid aluminum chloride in vacuum forelines and exhaust lines in vacuum systems of etching systems can include installing a trap just after the heated section of the piping line for trapping and removing aluminum chloride vapors from the effluent gas flow. As a result, the condensable aluminum chloride vapor is condensed and collected in the trap instead of depositing and building up in the piping lines. The trap can then be removed from the piping line whenever necessary for cleaning and removal of the deposited solid aluminum chloride.
The use of traps to remove condensable vapor from piping lines is well-known in the art. Conventional traps for trapping condensable vapor are often designed on the principle that lowering the temperature of the condensable vapor in the trap will cause the condensable vapor to condense as a solid. For example, U.S. Pat. No. 5,422,081, issued to Miyagi et al., discloses a trap device for a vapor phase reaction apparatus having an adjustable number of interior surfaces upon which the condensable aluminum chloride vapor cools on contact with the interior surfaces and condense on such surfaces. However, the Miyagi et al. trap requires a plurality of plate-shaped members assembled in layers, which can be difficult and time-consuming to manufacture and assemble. In addition, the large number of parts makes the Miyagi et al. trap difficult and time-consuming to disassemble for cleaning and removal of condensed aluminum chloride solids. Further, the close proximity between the plate-shaped members and the intake opening can cause the trap to clog prematurely, thus wasting a significant portion of the trap's volume.
Nor-Cal, Inc., of Yreka, Calif., has developed and manufactured a number of water-cooled traps for semiconductor processing equipment, including traps having coaxial and right angle configurations between the entrance ports to the traps and the exit ports to the traps. In the FTWA and FTWS series of traps manufactured by Nor-Cal, Inc., baffles redirect the gas flow between cooling coil tubes arranged cylindrically to increase the surface area for condensation of the condensable vapor flowing through the trap. Gas flowing into the trap is redirected either ninety degrees or one hundred eighty degrees by impacting either an interior surface of the trap or a cooling coil tube located in the trap. However, the Nor-Cal, Inc. trap, similar to many other conventional traps, becomes clogged near the entrance pipe to the trap, which results in low capacity and the need for frequent maintenance and cleaning.
U.S. Pat. No. 5,820,641 to Gu et al. describes a liquid cooled trap for collecting condensable vapor in a chemical vapor reaction system that comprises a first stage, which is a very poor heat exchanger, in order to avoid condensation of the vapor and the resulting solid deposits that could clog the entrance port to the trap, and a second stage which is a good heat exchanger and comprises cooling coil tubes and cooling cones or fins. However, due to the expense of the cooling coil tubes and cooling cones in the Gu et al. trap, the trap cannot be discarded when removal of the build-up of aluminum chloride is necessary. Therefore economic considerations require cleaning of the deposition surfaces in the Gu et al. trap so that the trap can be reused.
Since it is difficult to maintain all parts of an entire vacuum conduit system of an aluminum etching system at the proper temperature or to efficiently trap condensable aluminum chloride vapor with conventional traps, the buildup of solid aluminum chloride will inevitably occur throughout the vacuum conduit system of an aluminum etch system. Thus, at some point, the vacuum conduit system will require cleaning to remove the buildup of condensed aluminum chloride solids. This cleaning is usually carried out using water which, when contacted with aluminum chloride, results in the generation of tremendous amounts of toxic and corrosive hydrogen chloride (HCl) fumes and also generates a large amount of heat, both of which create hazardous conditions for workers.
Consequently, in spite of the heating jackets, heating tape, and various types of aluminum chloride traps already available, there is still a need for an improved trap that condenses and collects condensable aluminum chloride vapor produced in aluminum etching systems in an efficient manner and which allows for safer, easier, and more rapid removal and disposal of the deposited aluminum chloride solids from the trap, especially if such removal and disposal could eliminate the need to clean solid aluminum chloride deposits from deposition surfaces in such traps and from pipes in the vacuum forelines and exhaust lines of aluminum etch systems.